The state tax commissioner has the power to require any person engaged in such production, and the agent or employee of such person, or purchaser of such coal or commercial leonardite, or the owner of any royalty interest therein, to furnish any additional information the tax commissioner deems necessary for the purpose of correctly computing the amount of said tax; to examine the books, records, and files of such person; to conduct hearings and compel     the attendance of witnesses, the production of books, records, and papers of any person; and to make any investigation or hold any inquest deemed necessary to a full and complete disclosure of the true facts as to the amount of production from any coal or commercial leonardite mine or of any company or other producer thereof and as to the rendition thereof for taxing purposes.